Constant potential device



25, M. MORRISON CONSTANT POTENTIAL DEVICE Filed July 2, 1931 r 4/ ATTORNE Patented Apr. 25, 1933 MONTFORD MORRISON, OF MONTCLAIR, NEW JERSEY, ASSIGNOR TO LWESTINGHOUSE X-RAY COMPANY, INC., A CORPORATION OF DELAWARE CONSTANT POTENTIAL DEVICE Application filed July 2,

My invention relates to transformers and has particular reference to transformers utilized for heating the cathodes of thermionic discharge devices when such devices are employed to supply uni-directional cur rent to a load.

In systems of this type, wherein the dis charge device is employed as electric valves or rectifier tubes, the energy in flowing from a suitable source of alternating current to the load must flow through the rectifier tube, in order that the alternating current may be rectified and allowed to flow in only one direction. Due to the well known action of the electric valve or rectifier tube the electrical energy will flow between the elec trodes of the device during one half wave of the alternating current cycle and is suppressed duriiig the remaining half wave.

This action, therefore, of the valve tube permits the load to receive intermittent en ergy during only that half of the wave in which current flows between the electrodes of the valve tube. The time periods at which the load receives energy and the periods during which the energy is suppressed by the action of the discharge device depends upon the frequency of the alternating current source. The periods of time at which energy is supplied to the load and those during which it is suppressed are of such short duration, regardless of the frequency, that under most circumstances the fact that the load is supplied with intermittent energy is of no particular consequence.

Under other conditions, however, it is of considerable importance that the load should receive energy at a constant potential during the entire time of operation. This is particularly, true, for example, when, the load to which energy is supplied happens to be an X-ray tube. In utilizing X-ray tubes for radiographic or therapeutical purposes thetime of energization of the tube controls the period of exposure or treatment which must be maintained constant to obtain successful results.

It is accordingly an object of my invention to provide a transformer for supplying heating current to the cathode of a discharge 1931. Serial No. 548,281.

device which has inherent characteristics for maintaining a constant potential upon a load supplied through the discharge device.

Another object of my invention is the proconstant potential to a load during the wave of the alternating current cycle when the energy fromthe source is suppressed by the rectifier tube.

Still further objects of my invention will become apparent to those skilled in the art by reference to the accompanying drawing wherein:

Figure 1 is a diagrammatical representation of a system in which my device may be employed showing the transformer in cross section; and

Figure 2 is a cross section of my transformer taken on the line IIII of Fig. 1.

Referring now to the drawing in detail I have shown a source of alternating current potential such as a generator 5. A high tension transformer 6 has its primary winding 7 connected to the source 5 by means of conductors 8 and 9. A load 10 is supplied with energy from the secondary winding 12 of the transformer 6 by means of conductors 13 and 14 and the conductors 8 and 13 are connected to a common ground A thermionic discharge device 15 has its anode 16 connected to the conductor 14% and its cathode 17 connected to the load 10 by -means of a conductor 18. The discharge charge device to the load in a manner well known in the art.

A low tension transformer 19 is provided for supplying heating current. to the cathode 1T the discharge device. The primary winc ng 20 of this transformer is wound substantially the entire length of one leg of the closed iron core 22 and receives energizing current, by means of conductors 23 and 2 1, which are connected to the conductors 8 and 9 extending from the source 5. The secondary winding 25 of this transformer is connected to the cathode 17 of the discharge device by means of conductors 26 and 27 and the conductor 26 is connected to the load conductor 18.

A metallic shield 28 substantially surrounds the primary winding and extends longitudinally of the iron core 22 a greater distance than the primary winding. This shield provided with an air gap 29, as shown in Fig. 2, to prevent short circuiting of the electrostatic field created by this primary v-rinding. An insulating member 2-30 in turn surrounds this shielding member 28 and a second metallic shield 32 of conducting material is superimposed upon the insulating member and is likewise provided with an air-gap 33 (Fig. 2) to prevent short circuiting of the field set up by these windings. This latter shield 32 may be provided with outwardly flaring ends as shown at 3% to reduce the tendency of spark-over from these ends.

The secondary winding is wound upon the shielding member 32 for a substantial distance of the leg of the iron core 22, but does not extend as great a distance thereover as does the shielding member 28. This is likewise for the pn "pose of increasing the electrostatic capacity effect of the transformer.

It becomes readily apparent to those skilled in the art that the electrical energy from the secondary winding 12 is supplied to the load 10 and the rectifier device during each half wave of the alternating current cycle by means of conductors 13 and 1d. This circuit may be traced as follows: from the secondary winding 12 by means of conductors 13 to the load 10, conductor 18 to the cathode 17 of the discharge tube or rectifier 15, thence to the anode 1G and back to the secondary winding 12. During the remaining half-wave current will not flow through the rectifier 15 in the opposite lirection due to the valve action and hence no energy flows to the load.

The operation of my transformer may be described as follows: Vhen it is desired to energize the load a suitable switch (not shown) is first closed allowing energy to flow from the source 5 to the primary windings 7 and 20. The energization of the prinary winding 20 of transformer 19 energizes the secondary winding 25 and heats the cathode 17 to an electron emitting temperature. Energy will then flow from the secondary winding 12 of transformer 6 in the manner previously described through the device 15 during each half wave of the alternating current cycle.

During the remaining half cycle when the energy is suppressed by the action of the rectifier tube and, under normal circumtances no energy would How to the load, the transformer 19 will supply energy at a constant potential to the load. This is due to the inherent characteristics of the transformer 19 wherein an electrostatic capacity effect is prod ced in this transformer and energy is stored therein during the half wave in which energy flows to the load 10 from the secondary winding 12. The secondary winding 25 thus acts as the plate of a condenser and is positively charged when energy flows through the valve tube 15 while the primary winding 20, which is grounded at 11 acts as the remaining plate of the condenser and is negatively charged. This stored energy is then discharged into the load during the suppressed half wave through the conductors 26 and the grounded conductor 13.

This action of my transformer is analogous to a capacitance shown in dotted lines as being shunted across the load 10. The energy in flowing from the secondary winding 12 through the rectifier device 15 would, in this analogy, flow through the load and the capacitance during one half the wave and during the remaining half wave the capacitance would discharge into the load 10.

In the same manner the capacity stored in the transformer 19, due to the electrostatic capacity effect created by the elongated surface relation between the primary and secondary windings and/or the metallic shields 28 and 32, likewise discharges into the load during the suppressed half wave of the alternating current cycle. The primary winding 20 of the transformer 19 is grounded at 11 as well as the conductor 13 which extends from the load 10 thus completing a circuit to connect the windings of the transformer 19 across the load in the same manner as the respective plates of the capacitance I have found that by extending the wind ings a substantial distance over the iron core considerable capacity effect is 'oduced within the transformer. The 1)1'O\1S1011 of the metallic shields and extending the same longitudinally of the core a greater distance than the windings increases this effectto an extent equivalent to that which would be re quired for a capacitance shunted across the load in the manner previously described.

It can thus be readily seen that I have provided a transformer for supplying heating current to the cathode of a thermionic discharge device which has inherent characteristics producing an electrostatic capacity effect for supplying constant potential to a load. By employing this transformer in a system wherein the discharge device is utilized as a rectifier tube the load receives energy during half wave of the alternating current when energy from the normal source is suppressed by the action of the rectifier tube and a constant potential is thus supplied under all load conditions.

Although I have shown and described one specific embodiment of my invention I do not desire to be limited thereto as various other modifications of the same may be made without departing from the spirit and scope of the appended claims.

\Vhat is claimed is:

1. In combination with a unitary load, a source of alt rnating current therefor, a thermionic discharge device provided with a cathode to be heated for permitting current to flow to said load during one half wave of the alternating current cycle while suppressing the remaining half wave, and a transformer for heating the cathode of said device provided with a primary winding having an elongated surface area and a. secondary winding disposed relative to said primary winding and having an elongated surface area for producing an electrostatic capacity effect within said transformer to supply constant potential energy to said unitary load.

2. In combination with a unitary load, a source of alternating current therefor, a thermionic discharge device provided with a cathode to be heated for permitting current to flow to said load during one half wave of the alternating current cycle while suppressing the remaining half wave and a transformer for heating the cathode of said device provided with an iron core and a primary and secondary winding, the said primary and secondary windings extending a substantial CllSiZfi'lCG over the length of said core and presenting substantially equal surface areas to each other and to said core, for producing an electrostatic capacity effect within said transformer for supplying energy at a constant potential to said unitary load during the entire alternating current cycle.

3. In combination with a load, a source of alternating current therefor, a thermionic discharge device provided with a cathode to be heated for permitting current to flow to said load during one half wave of the alternating current cycle while suppressing the remaining half wave and a transformer for heating the cathode of said device comprising an iron core, a primary and a secondary winding extending a substantial distance over one leg of said core, and a shielding member interposed between said windings and extending a greater distance the length of said core than said windings, for produc ing an electrostatic capacity efiect internally of said transformer to supply energy to said load during the suppressed half wave to thereby supply a constant potential to said load during the entire alternating current cycle.

4. In combination with a thermionic discharge device provided with a cathode to be heated, a circuit for supplying electrical energy to a unitary load including, a source of electrical energy and said discharge device, a transformer for supplying heating current to the cathode of said device provided with a shield producing an electrostatic capacity efiect internally of said transformer for impressing a constant potential upon said unitary load.

5. In combination with a thermionic dis charge device provided with a cathode to be heated, a transformer for supplying electrical energy through said device to a unitary load, a low-tension transformer for supplying heating current to the cathode of said device, a source of commercial alternating current potential for energizing both of said transformers, said low-tension transformer being provided with shielding members producing an electrostatic capacity effect internally of said transformer for producing a constant potential at all loads.

6. In combination with a thermionic discharge device provided with a cathode to be heated, a circuit for supplying electrical energy to a unitary load having a conductor connected to ground, said circuit including a source of energy, said load and said dis charge device, and a low tension transformer provided with a primary winding connected to said source of energy and to ground and a secondary winding, for heating said cathode, and a shield disposed between said primary and secondary windings producing an electrostatic effectinternally of said low tension transformer for producing a constant potential under all loads.

In testimony whereof, I have hereunto subscribed my name this 24th day of June MONTFORD MORRISON. 

